Condenser tube protector



Jan. 15, 1963 J BAY CONDENSER TUBE PROTECTOR Filed Feb. 25. 1960 KAAA/AAAWAAAHAAAAANA \\\\\\\\\\\\\\\\\\s INVENTOR THOMAS J. BAY

ATTORNEYS United States Patent Ofilice 3,073,352 Patented Jan. 15, 1963 3,073,352 CQNDENSER TUBE PRQTECTOR Thomas 31. Bay, Rte. 1, Lynden, Wash. lFiled Feb. 25, 1960, Ser. No. 11,109 2 Claims. (Cl. 138-4140) Granted under Title 35, US. Code (1.952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

The present invention relates to condenser tube protectors and more particularly to new and improved condenser tube protectors in the form of inserts for preventing the corrosion and erosion of the tubes adjacent their inlet ends by water passing therethrough.

The condenser system in a ships boiler system generally includes a large number of small diameter tubes running between a pair of header plates and through which sea water is passed as a cooling medium. The tubes are generally of relatively constant diameter and as the water enters the tubes from outside the header plate, cavitation develops which tends to erode the inlet ends of the tubes. Furthermore, sea water contains various impurities which cause corrosion of the tubes, which when combined with the erosion due to cavitation, soon causes the tubes to leak, and requires that the tubes be replaced.

To eliminate the effects of erosion and corrosion of the tube ends, various types of protective inserts have been devised, but all have failed to render the required protection, at reasonable cost. In Patent No. 2,157,107, granted May 9, 1939, there is described a soft synthetic rubber tube end protector which was designed to prevent corrosion of the condenser tube ends. The rubber tube was capable of protecting the condenser tube since it had a high resistance to impingement erosion, however dimculty was encountered in developing a suitable method of securing the end protectors in place. The types of cement which were adequate to secure the soft rubber protectors in place complicated the insertion of the protectors into the tube ends.

Patent No. 2,195,403, granted April 2, 1940, was directed to a soft rubber protector secured by metal retaining bushings. This eliminated the necessity for using cement to secure the protectors in place. The rubber protectors secured by bushings complicated manufacture and increased the cost of production considerably.

In view of the difliculty of securing soft rubber protectors in place, tube end protectors constructed of Bakelite were next developed and tested. Patent No. 2,225,615, reissued as Re. 22,027 on February 17, 1942, covered protectors constructed of thermosetting materials such as Bakelite and also protectors constructed of hard rubber. As a result of tests of various materials of this type, large numbers of Bakelite protectors were made and put into service. In using the Bakelite protectors, however several unforeseen difliculties were encountered. Naval specifications and most commercial purchase requirements for condenser tubes permit an outside diameter tolerance of 5 to 6 thousandths of an inch. This, combined with a customary 5 percent over-weight tolerance. allows a variation in inside diameter up to about 14 thousandths of an inch. In view of the fact that thermosetting materials are rigid, having practically zero percement to keep the inserts in place. The small size inserts in the larger tubes created two new problems. First, the inside diameter of the tube was considerably greater than the inside diameter of the inner end of the insert, thus creating a hydraulic jump in diameter of the Water path. This effect was made worse by the fact that it was impossible to mold the thermosetting material to a thin edge at the inner end. Normally the innerends of the inserts were ground smooth with an edge thickness of 15-30 mils. This created turbulence with resulting cavitation and pitting action just beyond the insert. Furthermore, in cementing the insert in place, beads of cement were often left at the inner end of the insert by the workmen. The cement beads again caused turbulence and resultant erosion of the inner surface of the condensed tube. If no cement was used, corrosion often developed between the protective insert and the tube where it could not be seen and caused sudden tube failure, making it necessary for the entire condenser to be shut down for repairs. I

In order to seal the outer ends of the tubes, it was necessary to provide a flange at the outer end of the protector which would surround the tube end and seal against the header plate since it was impossible to provide a thermosetting protector which could conform to the varying flare shapes of the tube ends in the header plate. The flange of relatively brittle thermosetting material was therefore exposed to the incoming seawater. The incoming seawater often contained foreign objects which were dashed against the flanges by the force of the incoming water and caused the flanges to break, sometimes chipping the protector well inside the inlet of the condenser tube and allowing the impurities in the seawater and the turbulence caused by the irregularity to attack the tube.

In Patent No. 2,310,927, granted February 16, 1943, there is described still another type of protective insert. In this case, a transparent plastic material was chosen because it provided an easy means of checking the condenser tube wall under the insert without removing the insert. Various types of material were tried under operating conditions, but in time problems developed with each.

The insert described in Patent No. 2,310,927 was designed to be driven into the condenser tube thus obviating the need for cement. The material had to be deformable in order to force it into tubes of varying diameters within manufacturing tolerances. It needed to be heat resistant and resistant to oil and other contaminants in the circulating seawater. Several materials, which appeared to have the necessary properties, were chosen for use in accordance with the teachings of the patent but after several years of satisfactory service, became useless due to operating conditions.

The inserts were made with the aforementioned flange, which necessarily did not have support under the whole area between the header plate and the inside of the flange. Although the material was deformable to some extent, the flanges had to be hard enough to retain the seal between insert and plate. The hardness again led to breakage under repeated battering by foreign objects, such as driftwood, in the water. Furthermore, it was found that the varying conditions of heat also caused failure internally. Since the water in the tubes is seawater, the temperature of the water passing through the tubes is normally just slightly above that of the surrounding seawater under conditions of free flow operation. This presents no great problem since the surrounding water may vary from freezing to about F. depending on the location of the ship at the time. However various conditions cause extreme temperatures in the tubes. The steam which is being cooled by the tubes may be above 500 F. and if flow of the cooling water is stopped or slowed the temperature can approach that of the surrounding steam. For example, clumps of seaweed or schools of small fish are often encountered, which plug the holes in the inlet ends of the condenser tubes. At high temperatures, the resistance to creep of the material was lost and the seawater was enabled to attack the tube behind the protector.

In the present invention, there is provided a tubular shaped insert resembling to some extent the inserts described in the aforementioned prior patents, but which obviates the aforementioned disadvantages of the protectors described in them. The insert of the present invention makes use of a thermoplastic material which exhibits the required stiffness, resistance to creep, low coefficient of friction, and dimensional stability to allow the insert to be driven into the end of the tube and form a seal substantially along the entire length of the insert between the insert and the condenser tube. The material allows the insert to be made without the sealing flange at the inlet end of the insert and thus obviates the possibility of breakage due to objects striking the flange. Since the material conforms to the shape of the tube as it is driven in, and exhibits sufficient dimensional stability to allow molding to a feather edge at the inner end of the insert, the possibility of damage due to discontinuities in stream wall dimensions and cement heads is also eliminated.

Accordingly it is an object of the present invention to provide a condenser tube protector having improved impingement erosion and electrochemical corrosion resisting characteristics.

Other objects and many of the attendant advantages of this invention will be readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings wherein the single FIGURE is a view, partly in longitudinal section of an embodiment of the present invention.

Referring to the drawing, a condenser tube 11 is shown as being secured in a header plate 12 of a surface condenser, the-outer or inlet end of the tube being flared as indicated at 13. A tubular corrosion protector 14 fabricated from a material which is chemically inert with respect to the metal of the tube is frictionally secured within the inlet end of the condenser tube 11 with a drive fit. The material must have the physical characteristics of stiffness, recovery from deformation, excellent moldability, resistance to creep, tensile strength, low coeflicient of friction, fatigue endurance, toughness, dimensional stability, and abrasion resistance. A material which has these properties is Delrin,

CH O (CH O CH O which is described in the article entitled Delrin-a New Thermoplastic, by I. F. Cogdell and R. H. Hardesty, appearing in the Society of Plastic Engineers Journal, 'Vol. 14, No. 4, April 1958.

The outer (inlet) end of the protector 14 is flared slightly as at 16 to form a complete seal between the tube and the insert along the inner area of the tube. Due to the physical properties of the material used in fabrication of the insert, the flange, which was subject to breakage on the prior devices of this general type, is no longer required to seal the end of the tube.

The protector 14 is contoured so as to provide a restricted throat 17 and its internal diameter increases inwardly until it merges with the outside wall of the protector thus forming a feathered inner edge 18. The contour of the throat 17 corresponds substantially to the contraction and enlargement of a stream of water pass ing through an orifice, thereby minimizing turbulence and the liberation of air from the water and also eliminating impingement erosion and friction-loss in the jet of water entering the tube.

The protector insert is molded from the plastic material in the form of a cylinder having an outside diameter slightly larger than the largest internal diameter of the tubes which will be encountered. The physical properties of the material are such that with a cylindrical outside surface of constant diameter, the insert as it is driven into the condenser tube conforms to the irregularities of the tube in a manner to form a seal along substantially the entire length of the insert.

The insert herein described constitutes a decided advance in prolonging the life of surface condensers. The disadvantages of prior art devices of this type have been overcome in that the material used inherently forms an effective seal between condenser tube and insert, eliminating the possibility of the sea water attacking the tube inside the insert. The outside flange, which was subject to breakage in prior art devices, has been eliminated. The feather edge which may be obtained at the inner end of the insert and the lack of necessity of using cement prevent erosion beyond the insert which was prevalent with prior art protectors.

The increased reliability which is gained through use of the present invention is of the utmost importance in naval installations when, under conditions encountered in a naval engagement, the stresses and strains caused by rapid maneuvering might cause failure of partially deteriorated condenser tubes and the consequent disastrous shutdown of the propelling unit or units associated with such condenser. When it is considered that modern surface condensers may contain anywhere from 500 to 15,000 condenser tubes, the magnitude of the problem and the increased reliability ofiered by the present invention can be realized.

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed is:

1. A device for protecting from corrosion and erosion the inlet end of a tube extending through and secured to a header plate of a surface condenser and flared at its outer end, comprising a tubular member of Delrin,

CHgO CH O CH O inserted within the inlet end of said tube and engaging the inner wall throughout the length of the insert, said tubular member having an inlet end which conforms to the shape of said flare and is substantially coextensive with the inlet end of said tube, a throat of the venturi type adjacent said inlet end and having its smallest cross-section located substantially at the beginning of said flare, and having an internal diameter which increases inwardly until it merges with the outside wall of said insert in a feather edge.

2. A device as defined in claim 1 wherein said tubular member has an external diameter slightly larger than the internal diameter of said tube before insertion whereby the outside of said tubular member fits closely the inside surface of said tube when it is positioned therein.

Delrina New Thermoplastic, I. F. Cogdell and R. H. Hardesty, Society of Plastic Engineers Journal, volume 14, No. 4, April 1958 (copy filed in the Scientific Library). 

1. A DEVICE FOR PROTECTING FROM CORROSION AND EROSION THE INLET END OF A TUBE EXTENDING THROUGH AND SECURES TO A HEADER PLATE OF A SURFACE CONDENSER AND FLARED AT ITS OUTER END, COMPRISING A TUBULAR MEMBER OF "DERLIN," 